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| United States Patent |
5,037,560
|
|
Gayman
|
August 6, 1991
|
Sludge treatment process
Abstract
A process and apparatus for reducing sludges, especially those sludges
containing heavy metals and generated in electroplating, to a solid state
where the toxic constituents of the waste are prevented from leaching. The
process involves mixing a metallic soap or hydroxide with the sludge and
then using low-temperature induction heating to form coacervate bonds that
encapsulate the toxic waste particles in a pumice-like matrix. The
apparatus allows a small amount of metallic soap to be thoroughly mixed
through sludge and a continuous ribbon of the resulting putty-like waste
to be fed into a series of microwave drying ovens and evacuation chambers.
After the drying and dewatering sequences, the apparatus extrudes a
pumice-like solid suitable for disposal in accordance with EPA
regulations.
| Inventors:
|
Gayman; Danny (24104 11th Ave. South, Des Moines, WA 98198)
|
| Appl. No.:
|
491070 |
| Filed:
|
March 9, 1990 |
| Current U.S. Class: |
405/129.27; 210/739; 210/748; 210/749; 210/758; 210/766; 405/129.3 |
| Intern'l Class: |
B01D 001/24 |
| Field of Search: |
210/748,749,751,758,766,767,770,774,737,729
252/301.18,632
110/229
|
References Cited
U.S. Patent Documents
| 4043047 | Sep., 1977 | Galliker | 210/748.
|
| 4221680 | Sep., 1980 | Hardwick et al. | 252/632.
|
| 4242220 | Dec., 1980 | Sato | 252/632.
|
| 4615809 | Oct., 1986 | King | 210/751.
|
| 4927564 | May., 1990 | Barlou et al. | 210/729.
|
Other References
EPA/530-2W-88-009-1, Best Demonstrated Available Technology (BDAT) Document
for F006, vol. 12, (Proposed, May 1988, 40 CFR & 1.268 Appendix 1-Toxicity
Characteristics Leaching Procedure.
|
Primary Examiner: Dawson; Robert A.
Assistant Examiner: Reifsnyder; David
Attorney, Agent or Firm: Bohan; Thomas L.
Claims
I claim:
1. Process of treating a leachable, heavy-metal waste sludge, wherein said
waste sludge is in solution, said process comprising the steps of:
a) mixing a quantity of metal with said waste sludge to form a homogeneous
mixture; and
b) adding heat to said homogeneous mixture by low-temperature heating means
so as to induce a chemical reaction between said metal and said waste
sludge, leading to the formation of a dried, leach-resistant solid.
2. Process of claim 1 wherein said low-temperature heating means is
combined with a means of separating solvents removed from said waste
sludge during heating.
3. Process of claim 2 wherein said low-temperature heating means comprises
microwave radiation.
4. Process of claim 2 in which said metal is aluminum.
5. Process of treating waste sludge comprising:
a) mixing a quantity of metallic soap or hydroxide to a waste sludge to
form a homogeneous mixture and;
b) adding heat to said homogeneous mixture by low-temperature induction
heating means.
6. Process of claim 5 in which said metallic hydroxide is aluminum
hydroxide.
7. Process of claim 5 in which said metallic soap is aluminum stearate.
8. Process of claim 5 in which said metallic soap is aluminum oleate.
9. Process of claim 5 in which said metallic soap is aluminum palmitate.
10. Process of claim 6 where the quantity of metallic soap or hydroxide is
between 0.1% and 2.0% by weight of the sludge.
11. Process of treating waste sludge consisting essentially of:
a) contacting said waste sludge with an aluminum compound, wherein the
quantity of said aluminum is between 0.1% and 2.0% by weight of said waste
sludge; and
b) sequentially irradiating said mixture with microwave radiation and
removing separated solvents and repeating said sequence until said mixture
forms a solid pumice-like waste matrix.
12. Automatic and continuous process of sludge waste reduction comprising
the steps of:
a) mixing a metallic soap or hydroxide with said sludge waste resulting in
a mixture;
b) extruding said mixture in a continuous ribbon;
c) initially induction-heating said mixture;
d) separating solvents from said mixture using a plurality of alternating
chamber pairs wherein one chamber in each of said pair provides a means
for separating solvents from said mixture while a second chamber in each
of said pairs provides a means of induction-heating said mixture;
e) venting and draining said solvents;
f) storing a solid mixed sludge waste product for transport;
g) continuously transporting said continuous ribbon of said mixture through
said initial induction-heating and said alternating chamber pairs to
storing means.
13. Process of claim 12 in which said metallic hydroxide is aluminum
hydroxide.
14. Process of claim 12 in which said metallic soap is aluminum stearate.
15. Process of claim 12 in which said metallic soap is aluminum oleate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the treatment of industrial waste, especially
sludge generated by electroplating operations. More particularly, this
invention consists of a process and apparatus designed to deal with that
form of electroplating waste designated by the U.S. Environmental
Protection Agency (EPA) as F006 sludge. The objective achieved by the
invention is the stabilization of F006 sludge against leaching--as
measured by the Toxic Characteristic Leaching Procedure (TCLP) [40 CFR
.sctn. 1.268, Appendix 1 (7-1-88)]--to the degree that the treated
material meets EPA leach-resistant requirements for landfill disposal
pursuant to the Hazardous and Solid Waste Amendments of 1984 (HSWA) [98
Stat. 3221] and to the Resource Conservation and Recovery Act of 1976
(RCRA) [U.S. Code 1982 Title 42 .sctn. 6901 et seq. Oct. 21, 1976, P.L.
94-580, 90 Stat. 2795].
Industrial waste disposal is becoming ever more tightly regulated,
especially with respect to land disposal in sanitary land fills. The EPA
is required to classify hazardous wastes and to prohibit their land
disposal unless certain very stringent conditions are met. For the
purposes of the present invention, the wastes generated by industrial
electroplating are of particular interest. Such wastes have been divided
into different categories, depending on the identity of their major
constituents and the specific electroplating process producing them. These
categories are denominated as F006, F007, F008, . . . F0mn. [See, for
example, EPA/530-SW-88-0009-I, Best Demonstrated Available Technology
(BDAT) Background Document for F006, Volume 13 (Proposed), May 1988.]
Although the present invention is directed toward F006 wastes, it can be
modified to deal with several of the other F0mn categories as well. F006
sludge is broadly defined in 40 CFR .sctn. 1.268.10 as:
Waste-water treatment sludges from electroplating operations except from
the following processes: (1) Sulfuric acid anodizing of aluminum; (2) tin
plating on carbon steel; (3) zinc plating (segregated basis) on carbon
steel; (4) aluminum or zinc-aluminum plating on carbon steel; (5)
cleaning/stripping associated with tin, zinc and aluminum plating on
carbon steel; and (6) chemical etching and milling of aluminum.
Electroplating is key to a wide range of industry because it enables one
to: (1) provide corrosion protection for a multitude of items; (2) control
the surface resistivity of electronic devices; (3) apply a decorative or
functional coating to a myriad of items. Since the electroplating industry
is a sizable part of the industrial economy and electroplating by its
nature creates a high volume of hazardous waste by-products, anything
which limits the freedom of the industry to dispose of such by-products
has a very high economic impact. Viewing the problem from a different
perspective, one notes the extreme importance to society's general
well-being that hazardous wastes be disposed of in a manner which
minimizes the air and water release of the toxic, mutagenic, teratogenic,
and carcinogenic components of that waste. The U.S. Congress through the
EPA has ruled that such waste, before it can be deposited in landfills
where it eventually will be exposed to leaching agents (primarily water
run-off), must be able to pass stringent tests of stability with respect
to potential leaching of any "scheduled" compounds. These tests are
codified by the EPA in terms of TCLP toxicity levels which the waste must
not exceed if it is to be directly deposited into a sanitary land
fill--the only practical disposal mode in view of the total annual tonnage
involved.
Specifically, the invention calls for thoroughly mixing extraordinarily
small quantities of certain metal salts, in particular metal soaps--salts
of the fatty acids such as stearic acid, oleic acid, and palmitic
acid--with the sludge, extruding the mixture, and then transferring energy
to it by induction heating at relatively low temperatures. The water which
is forced to the surface of the extruded sludge mixture--as the result of
the heating and the formation of hydrophobic bonds--is removed in part by
evacuating the region around the product. It is also removed in part by
direct mechanical methods, thus reducing the total heat which must be
introduced. It is apparently the removal of free and loosely-bound water
and the formation of micro-matrices within the extruded sludge that
effectively binds the waste's toxic components to the degree that the end
product passes the TCLP tests.
2. Description of Prior Art
Even though it is only relatively recently that the F006 disposal situation
has become extremely acute, the problem of what to do with
heavy-metal-contaminated effluent streams has confronted the metal-plating
and electronics industries for years. One early approach to the problem
was simply to dry the sludge in large conventional ovens and then to place
it in landfills. This action implied a certain obliviousness to the
leaching dangers, since conventional drying does not detoxify
electroplating sludges to the point where they can be safely deposited in
landfills. The inadequacy of this technique is clear in the light of the
EPA standards referred to above. Sludges treated simply by conventional
heating are not able to comply with the TCLP-based criteria set out by the
EPA.
Recognizing the inadequacy of conventional drying, the industry turned to
techniques involving the precipitation of heavy metal compounds from the
raw sludge so as to produce cleaner material for disposal. Of course, one
of the by-products of such precipitation is itself hazardous sludge,
sludge which though smaller in volume than the original material, contains
a higher concentration of hazardous compounds and hence has a higher
specific toxicity. Thus, the precipitation approach simply shifted to a
new arena the waste treatment problem presented by the sludge.
It was in that context that the EPA published EPA/530-SW-88-0009-I, Best
Demonstrated Available Technology (BDAT) Background Document for F006,
which summarized current F006 treatment methods. The methods which that
document sets out for treating electroplating waste can be categorized as:
stabilization, vitrification, and high-temperature metal recovery. Of
these, the only realistic methods at present involve stabilization.
Stabilization methods work by locking the sludge's hazardous materials in
place rather than removing or chemically modifying them. Prior
stabilization methods have required that one add large quantities of a
stabilizing compound such as Portland cement to the sludge, and then cure
the mixture. Leaching of metals and other toxic substances from the
resulting waste is then impeded by the entrapment of those substances
within the solid matrices established throughout the sludge by the
stabilizing agent.
There are four serious drawbacks associated with traditional stabilization.
First, it requires de-watering of the sludge as a prerequisite. The
conventional methods of de-watering sludge include pressing, centrifuging,
and conventional heat drying: all are time-consuming and expensive.
Secondly, the addition of the stabilizing agent increases the weight and
volume of sludge by a great deal, up to 150%. The increase in the amount
of waste to be deposited is a serious problem, both in terms of shipping
expense and allocation of scarce landfill space. Thirdly, traditional
stabilizing methods require a long curing period. In addition to the time
required to treat each load of sludge, vast amounts of energy are used by
the drying ovens. Lastly, traditional stabilization methods result in a
waste product with little physical integrity, a situation which leads to
crumbling and the production of large quantities of toxic dust and larger
fragments. Not only are the toxic dust and fragments hazardous to
personnel transporting and disposing of the waste, but the fragmentation
increases the surface area exposed to leaching agents after disposal into
the landfill and hence increases the likelihood of subsequent leaching.
An example of a stabilizing process requiring both the pre-treatment of the
sludge and the addition of significant amounts of a thermoplastic
stabilizing agent is described in U.S. Pat. No. 4,242,220 issued to Sato
in 1980. Sato teaches a method of treating waste sludge requiring the
following sequence of steps: (1) pre-treating the waste sludge until its
water content is not greater than 13%, (2) using microwave radiation to
weaken the coalescence between the sludge particles to the point where a
powder results, (3) mixing a thermoplastic resin with that powder, (4)
using microwave radiation to melt the resin so as to trap the sludge
particles in an insoluble capsule, and (5) cooling and molding the mixture
into a solid mass. In addition to being limited to sludge with a low water
content and the fact that significant volume is added to the waste
product, the Sato process requires two drying steps. (It is true that Sato
utilizes microwave rather then conventional heating, a fact that within
the context of the process provides a reduction in the total electrical
energy required. It appears that the use of the heat is to effect physical
rather than chemical change in the mixture, in distinction to the use of
microwaves in the present applicant's invention.)
An example of a stabilizing process which requires the addition of large
quantities of a glass-like stabilizing agent and which ultimately results
in a brittle waste product is described in U.S. Pat. No. 4,221,680 issued
to Hardwick in 1980. Hardwick teaches a radioactive waste sludge treatment
requiring the following sequence of steps: (1) injecting a slurry
containing radioactive wastes into open glass slugs, (2) placing the
filled slugs in a microwave oven to dry the slurry while venting gases out
of the oven and (3) fusing the dried slurry within the glass slug to
produces a glass-like solid material. Although the Hardwick process
appears to be able to handle sludge with a high water content, the dried
slurry is not disposable until it has been fused with the glass slug. Not
only does the glass add substantial volume to the waste product, but it
has the additional disadvantage of providing only a brittle shell between
the environment and the toxic slurry.
Apparatus to extrude sludge onto a belt and through a dryer system are
generally recognized art. U.S. Pat. No. 4,043,047 issued to Galliker in
1977 discloses apparatus for reducing watery sludge to a friable mud. This
apparatus utilizes a conventional drying process which would not be
suitable for F006 sludge. It encompasses a piston pump extruder and an
electrolytic heat treatment unit connected by a conveyor belt. It appears
that the only way to adapt the Galliker apparatus to handle waste with
different characteristics is by adjusting the speed of the pump so as to
vary the quantity of materials per unit of time passing through the drying
chambers.
What is needed is a waste treatment process that can treat toxic sludge
possessing a high and variable water content so as produce a readily
disposable, cohesive solid waste product without significantly increasing
the total weight or volume to be disposed of. Furthermore, a waste
treatment apparatus is needed which is easily adapted to the landfill
preparation of electroplating wastes possessing a wide variety of physical
and chemical characteristics.
SUMMARY OF THE INVENTION
The invention encompasses an industrial waste-treatment process and the
apparatus devised for utilizing that process. Its object is to reduce the
hazards associated with heavy metal sludge wastes to the point where the
resultant product is acceptable for land disposal in accordance with U.S.
Environmental Protection Agency regulations and, moreover, to do this
without the weight increase inherent in traditional treatments of such
sludges. This objective is accomplished by forming hydrophobic coacervate
bonds throughout the waste in such a way that a relatively lightweight
solid, resistant to leaching and dusting, results. More particularly, the
sludge is first mixed with a small amount of a metallic soap or hydroxide
such as aluminum hydroxide. The mixture is extruded as a thin ribbon into
the inlet port of an apparatus consisting of an alternating series of
induction heaters and vacuum chambers which have the effect of adding at
only slightly elevated temperatures the energy necessary to complete the
coacervate bonding while removing the water forced to the surface of the
ribbon by the heating and chemical reaction. The substance produced at the
outlet of this apparatus is a dry, pumice-like substance capable of
meeting the EPA's TCLP criteria and suitable for shipping to a disposal
site. Pivotal to the practicality of the invention is the fact that its
process for stabilization adds very little to the weight and the volume of
the product to be disposed of.
The key to the invention is the high efficiency with which it enables
metallic soaps to form leach-resistant matrices for the various sludge
constituents which need to be stabilized. This efficiency is measured both
by the lightness of the final product and by the very short time which is
required to achieve that final product. Part of this efficiency is related
to the method by which energy is added to establish the matrix-forming
bonds. By using induction heating, a low-temperature energy transfer can
be accomplished. To achieve a comparable energy transfer using
conventional ovens would require either a much longer time or a much
higher temperature. Higher temperatures cause a breakdown of the sludge
components, producing dusting, among other undesirable results. The
disadvantages of an increased processing time are obvious.
The sludge as received can contain a significant amount of water, both free
and as loosely-bound waters of hydration. Aqueous solutions of metallic
soaps are then added to the sludge, leading to the formation of coacervate
bonds between the metallic soaps and the sludge. Because these bonds are
hydrophobic, one of their effects is to force the free and loosely-bond
water molecules out of the sludge. These water molecules then appear on
the surface of the sludge ribbons. As the sludge ribbons are alternately
passed through induction heating zones and vacuum drying zones, the water
is sequentially driven up to the surface and then evaporated or simply
wiped off by mechanical means. Because of the modular nature designed into
the total apparatus, the system can be adapted to a variety of sludge
characteristics: induction heating zones and vacuum drying zones can be
added or subtracted.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of the apparatus used to carry out the
process claimed.
FIG. 2 is a flow chart of the steps of the treatment process.
PREFERRED EMBODIMENT OF THE INVENTION
1. The Apparatus
FIG. 1 depicts the preferred embodiment of a sludge processor 1. In its
preferred embodiment the sludge processor 1 comprises a conventional
industrial mixer 2, a sludge extruder 3, a primary induction heating
chamber 4, vacuum and induction heating chamber pair 5, and a sludge
transport container 6. Waste sludge is transported through said sludge
processor 1 by a conveyor belt 7.
Said industrial mixer 2 is a crucial element of the invention because
thorough mixing is essential to the process for which said sludge
processor 1 is to be used. Said primary induction heating chamber 4 is
comprised of an oven 8a. Said vacuum and induction heating chamber pair 5
is comprised of a vacuum evacuation chamber 9 and an oven 8b. Said vacuum
evacuation chamber 9 drains into a condensing unit 10. In its preferred
embodiment, said condensing unit 10 filters and then vents non-toxic gases
and solvents into the outside atmosphere.
Because sludge is a highly variable mixture, a significant attribute of
said sludge processor 1 is its modularity. The number of vacuum and
induction heating chamber pairs 5 can be increased or decreased quickly
and easily to handle the volume and characteristics of the specific sludge
to be handled.
2. The Process
Said sludge processor 1 is designed to process heavy metal sludge wastes
generated by electroplating industries. The process is designed to result
in a waste product capable of meeting the requirements of the TCLP. The
steps shown in FIG. 2 are further described as follows:
(a) Mixing
A sludge with a water content as high as 95% is thoroughly mixed with a
small quantity of a metallic soap. The amount and type of said metallic
soap depends on the volumes and characteristics of said sludge to be
processed. However, extremely thorough mixing results in the use of
smaller quantities of said metallic soap and better chemical bonding. The
rule of thumb is that one-tenth (1/10) to one-quarter (1/4) the quantity
of metallic soap will provide the same leaching characteristics with
thorough mixing as is required without said mixing. Aluminum hydroxide
works well with F006 sludges.
A major advantage of this process is that a successful bonding reaction is
not dependent on the pH of said sludge. F006 sludge usually has a pH
ranging from 7.8 to 12.5. Though a pH of 11 produces optimum
solidification, the precise control of pH is not necessary to achieve
desired bonding. A paste-like mixture of sludge and metallic soap may then
result from said mixing step.
(b) Extrusion
Said paste-like mixture of sludge and metallic soap is extruded as a
ribbon. The dimensions of said ribbon vary depending on the
characteristics of said sludge. A width of 12 inches and a thickness of
one-quarter (1/4) inch works well for processing of approximately 50
pounds per hour systems.
(c) Heating
Said ribbon is then heated by induction but in such a way that the surface
temperature does not exceed 100.degree. C. This allows enough energy to be
added to melt said metallic soap. As said metallic soap melts it forms
durable hydrophobic coacervate bonds and in this way establishes a
multitude of cages around the toxic particles of said sludge.
It is in fact crucial to the process that the temperature of said
paste-like mixture of sludge and metallic soap not exceed 100.degree. C. A
low drying temperature will de-water said ribbon of said paste-like
mixture of sludge and metallic soap resulting in a cohesive pumice-like
solid. In contrast, high drying temperatures produce a brittle waste
product or toxic dust.
(d) Separation-of-Solvents
Said induction heating is accelerated by removing solvents, largely water,
from said ribbon. Said bonding reaction between said metallic soap and
said sludge is hydrophobic and forces free and loosely bonded water
molecules out of said ribbon, whereupon said water molecules can then be
mechanically removed. Solvent removal rates as high as 6500 grams per hour
for 1000 watts of input microwave power have been achieved. A major
advantage of this process is that said ribbon does not have to be
pre-dried to a specific moisture level before being processed so as to
pass said TCLP.
(e) Repetition
Sequential repetition of said heating and said separation-of-solvents steps
results in a cohesive pumice-like solid waste product.
(f) Testing
The TCLP involves reducing the particle size of a EPA regulated waste and
defining the elements of said EPA regulated waste by analytical methods.
The success of the process is determined by comparing the results of said
TCLP to EPA regulations which are set out in terms of TCLP toxicity
levels.
(g) Secondary Spraying
If said cohesive pumice-like solid waste product fails to meet EPA
regulations, a solution of 3 percent aluminum soap (aluminum reacted with
long-chain fatty acids typically used in soap manufacture) dissolved in
isopropyl alcohol is sprayed over the surface of said cohesive pumice-like
solid waste product. After curing for 24 to 48 hours, said cohesive
pumice-like solid waste product will pass said EPA regulations for TCLP
testing.
In an alternative to the preferred embodiment, said sludge processor 1
additionally comprises two vacuum boxes and an adsorbent conveyor belt,
wherein said adsorbent conveyor belt carries said waste sludge over said
vacuum boxes. The alternative to the preferred embodiment also comprises
an air draw 11 on each oven 8 to remove contaminated air from said ovens
8, through an activated carbon filter and to exhaust the filtered air.
3. Examples of Process Using Typical F006 Sludge
EXAMPLE 1
Sludge Composition No. 1
The first example of the effectiveness of the Process involved the
treatment of an F006 sludge at 11.9% solids, by weight, and a pH of 7.9.
The solids content included:
______________________________________
Chromium (Cr) 38,500 parts per million (ppm)
Copper (Cu) 4,200 ppm
Cadmium (Cd) 120 ppm
Lead (Pb) 310 ppm
Zinc (Zn) 245 ppm
Aluminum (Al) 122,000 ppm
Iron (Fe) 14,300 ppm
Cyanide (CN) 14 ppm
______________________________________
Aluminum stearate was added to Sludge Composition No. 1, in quantities
ranging from 0.1% to 2.0% by weight of sludge. The sludge and aluminum
stearate were mixed and the resulting material pressed to a ribbon 12
inches wide and one-quarter (1/4) inch thick. The ribbon was continuosly
dried in the manner indicated in steps 2c. and 2d. of the Process. A
comparison of the TCLP results for the sludge dried, but without aluminum
stearate treatment and the sludge dried after treatment (for a 0.1%
quantity of aluminum stearate only) are provided in Table 1. The solvent
removal efficiency, measured as a function of the drying process time, and
determined as a function of the quantity of aluminum stearate added to the
sludge, is provided in Table 2.
TABLE 1
______________________________________
Results of TCLP testing for aluminum stearate treated
(0.1% by weight) and untreated Sludge Composition No. 1.
0.1% alum. stear.
Untreated
Leachate treated sludge
sludge
______________________________________
Cr 0.012 ppm 2.21 ppm
Cd 0.005 ppm 0.64 ppm
Pb 0.018 ppm 3.14 ppm
Cu 0.043 ppm 0.88 ppm
Zn 0.011 ppm 1.23 ppm
______________________________________
Note: All other aluminum stearate quantities evaluated (0.2%, 0.5%, 1.0%
and 2.0%) met EPA regulation levels.
TABLE 2
______________________________________
Solvent removal rates for six quantities of aluminum
stearate mixed with Sludge Composition No. 1.
Amt. of alum. stear.
Grams solvent removed
Final solids
added to sludge
per KWH of energy in
content sludge
______________________________________
0.0% (by wt.)
1018 85.8%
0.1% 1440 86.2%
0.2% 1792 86.8%
0.5% 2464 86.6%
1.0% 3182 86.9%
2.0% 3740 87.4%
______________________________________
Untreated sludge, dried as indicated in steps 2c. and 2d. of the Process,
was sprayed, following step 2g. of the Process, with a solution containing
3.0% aluminum stearate dissolved in isopropyl alcohol in a ratio of five
grams of the solution to 200 grams of dried sludge. The sprayed sludge was
cured for 24 hours at room temperature and TCLP tested. The results are
presented in Table 3, with a comparison to TCLP results for the dried,
untreated sludge.
TABLE 3
______________________________________
Results of TCLP testing for dried, untreated Sludge Composition
No. 1, and the same sludge dried, and then sprayed with 3.0%
aluminum stearate in isopropyl alcohol and cured for 24 hours
at room temperature.
3.0% alum. stear.
in isopr. alc. spray
Untreated
Leachate treated sludge
sludge
______________________________________
Cr 0.114 ppm 2.21 ppm
Cd 0.022 ppm 0.64 ppm
Pb 0.018 ppm 3.12 ppm
Cu 0.210 ppm 0.88 ppm
Zn 0.120 ppm 1.23 ppm
______________________________________
EXAMPLE 2
Sludge Composition No. 2
The second example of the effectiveness of the Process involved the
treatment of a heavy metal sludge at 14% solids, by weight, and a pH of
7.9. The solids content included:
______________________________________
Cr 4,200 ppm
Cu 31,500 ppm
Cd 2,850 ppm
Pb 240 ppm
Mercury (Hg) 8 ppm
Zn 850 ppm
______________________________________
The sludge was dried, following steps 2c. and 2d. of the Process, to a
solids content of 88% by weight and tested by the TCLP for leachate
levels. This batch of sludge was then mixed in a one-to-one ratio with dry
cement dust, per EPA BDAT recommendations, and allowed to cure for 48
hours. It was then tested by the TCLP for leachate levels. Results of
these tests are provided in Table 4.
Also provided in Table 4, are the results of TCLP testing of Sludge
Composition No. 2 after treatment with aluminum hydroxide. Specifically,
1.0% of aluminum hydroxide solids was added, as a 50% paste in water, to
the sludge and mixed per step 2a. of the Process. The treated sludge was
extruded and microwave dried per steps 2c. and 2d. of the Process, to an
80% solids content. The treated and dried sludge was tested by the TCLP
for leachate levels.
TABLE 4
______________________________________
Results of TCLP testing for aluminum hydroxide treated,
untreated, and EPA-BDAT treated Sludge Composition No. 2.
1.0% alum. hydrox.
untreated BDAT treat
Leachate
untreated sludge
sludge sludge
______________________________________
Cr <0.01 ppm 2.65 ppm 1.85 ppm
Cd <0.01 ppm 0.08 ppm 0.04 ppm
Pb <0.01 ppm <0.01 ppm <0.01 ppm
Cu 0.15 ppm 4.50 ppm 3.68 ppm
Hg <0.01 ppm <0.01 ppm <0.01 ppm
Zn <0.01 ppm 1.95 ppm 0.02 ppm
______________________________________
It is to be understood, of course, that the foregoing description relates
to particular embodiments of the general invention and that modifications
or alterations of these embodiments may be made without departing from the
spirit or scope of the invention as set forth in the appended claims.
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